[pymvpa] reverse mapping searchlights with center_ids

[kimberg at mail.med.upenn.edu]

Yaroslav Halchenko:
> myds_sl = np.zeros((myds.nfeatures,))
> myds_sl[center_ids] = sl_map
> mymap = myds.mapReverse(myds_sl)

thanks, that seems like an improvement, i'll test it and use it.

dan